Bombesin-like peptides are uniformly thought to act as mitogens in cancer. Yet by studying human tissues we have recently shown that bombesin and its mammalian homologue gastrin-releasing peptide act as morphogens, promoting tumor differentiation when aberrantly up-regulated in colon cancer. In contrast, little is known about the bombesin-like peptide neuromedin B (NMB) and its receptor (NMB-R) in the human gastrointestinal tract. We therefore studied their presence and function in normal and malignant human colonic epithelia. Anti-NMB monoclonal antibodies were made against KLH-conjugated human NMB; while Anti-NMB-R antibodies were raised in rabbits against KLH-conjugated peptides corresponding to the 3^rd intracellular loop and C-terminal tail of the receptor protein. NMB antibody recognized two bands at ~1.2 kDa and ~1.5 kDa. NMB-R antibodies recognized a band at 80 kDa (predicted 43 kDa); while treatment with the de-glycosylating agent PNGase F generated bands at 65, 47, and 43 kDa. By immunohistochemistry, both NMB and NMB-R were expressed in normal and cancerous colonic epithelial tissues. In cancer, the amount of NMB was similar to that expressed by proliferating epithelial cells located within the crypt. In contrast, NMB-R expression was increased in cancer, with higher levels detected in better differentiated tumor cells. To assess NMB function, proliferation was determined in the non-malignant human colonic epithelial cell line NCM460 and in the colon cancer cell lines Caco-2 and HT-29. Exogenously added NMB was 50-100% more efficacious than gastrin-releasing peptide in causing tumor cell proliferation; while only NMB increased NCM460 cell proliferation. These findings indicate that NMB and its receptor are coexpressed by proliferating cells where they act in an autocrine fashion with similar and modest potency in both normal and malignant colonic epithelial cells.